1. Field of the Invention:
The present invention relates to a cardiac output measurement method and a system for the application of the same, which are used to, for instance, examine the cardiac function or to control cardiac output during or after a heart operation.
2. Description of the Prior Art:
When cardiac output is to be measured for the purpose of, e.g., examining the cardiac function, by a right heart catheterization, the conventional practice is to employ an indicator dilution method. There are various forms of the indicator dilution method, and they include thermodilution in which the cardiac output is obtained from thermal diffusion, and dye dilution in which the cardiac output is obtained from changes in illuminance due to dye diffusion. Among these, the thermodilution, which is relatively closely related to the present invention, will be described.
When a right heart catheterization is performed utilizing thermo dilution, a catheterization is introduced in such a manner that its distal end is positioned in the pulmonary artery while its injectate injection port is positioned in a right atrium.
FIG. 4 illustrates the manner in which a catheter is introduced according to the prior art. Specifically, a catheter K is introduced from, e.g., a juglar vein, femoral vein or basilic vein. It is then passed through the superior or inferior vena cava, then through the right atrium RA and the right ventricle RV, and is held in place with its distal end positioned in the pulmonary artery. The catheter K has an indicator charge port positioned in the right atrium RA, and a thermistor T positioned in the pulmonary artery.
When an indicator (i.e., an injectate) the temperature whereof is higher or lower than the blood temperature is introduced from the charge port of the catheter K toward the right atrium RA, as the injectate diffuse through the right atrium RA and the right ventricle RV, the temperature of the injectate is diluted. The diluted temperature of the injectate is sensed by the thermister T positioned in the pulmonary artery. The sensed temperature is calculated to obtain a curve expressing the diluted temperature, i.e., a curve expressing changes in the blood temperature with the passage of time, such as that shown in FIG. 5. The area (hatched in FIG. 5) defined by the obtained curve is used in the following equation (1) developed by Stewart Hamilton, from which the cardiac output is calculated. ##EQU1## where C. O.: cardiac output, Si: specific gravity of injectate liquid, Ci: specific heat of injectate, Vi: amount of injectate, Ti: temperature of injectate, Tb: temperature of blood, Sb: specific gravity of blood, Cb: specific heat of blood, and .intg..infin..DELTA.Tbdt: area of thermodilution curve.
Described above is an example a cardiac output measurement which has conventionally been performed by utilizing the thermodilution. The present applicant has already filed in Japan an application for patent through a cardiac output measurement system capable of performing cardiac output measurement continuously (the application was laid open as Japanese Patent Laid-Open No. 125329/1986).